(1) Field of the Invention
The invention relates to guided underwater objects (GUOs), particularly (although not exclusively) unmanned, self-propelled, underwater objects, which are useful for performing tasks such as carrying out underwater surveys and conveying equipment or other payloads.
(2) Description of Related Art
Current technology includes ROVs and UUVs for civilian offshore survey and intervention tasks, as well as UUVs such as the RCMDS2.
Common features of known GUO-systems are:                (a) Acoustic tracking systems are used to measure position and movement and enable a vehicle operator to maintain positional control of the GUO;        (b) Onboard sensors (e.g. sonar/camera) used for GUO control during final approach and during intervention type operations;        (c) Fibre-optic or copper umbilicals used for transmitting sensor data back to an operator and control signals to the GUO system.        
There are several limitations resulting from the known systems, viz:                (a) the inclusion of fibre-optic/copper communications links, sonars, cameras and acoustic tracking transponders result in complex and expensive systems. In applications where (for one shot systems) the vehicle is not recovered at the end of an operation this enhanced level of cost is undesirable.        (b) the update rate of the tracking system is limited by the speed of sound in water, with the resulting time delay in obtaining an accurate measurement effectively limiting the maximum safe movement speed of the GUO and the rate at which its positional control loop can be updated. This is turn reduces the ability of the GUO to operate effectively in higher currents and levels of turbulence.        (c) Umbilicals deployed from GUOs are prone to entanglement, whilst disposable fibres used on some GUO systems can result in large lengths of fibre-optic cable being left in the sea at the end of a mission, which is not environmentally acceptable.        